1. Field of the Invention
The present invention relates to refrigerated vending machines and, more particularly, to power-conserving refrigerated vending machines. A major objective of the present invention is to provide continuous availability of cold product with temporarily reduced power consumption.
2. State of the Art
Vending machines provide for cost-effective delivery of consumer items. In principle, they provide full-time product availability with minimal intervention by a human operator. However, full-time operation can result in wasted energy consumption as the machine may be on for long intervals of inactivity. The concern for energy consumption is especially acute in the case of refrigerated vending machines.
Refrigerated vending machines maintain their contents below ambient temperatures. There can be various reasons for keeping the dispensable items cold. Cold generally helps preserve perishable food items. In some cases, for example, with soda and other beverages, the items may taste better chilled. In other cases, the refrigerated vending machine can be used in conjunction with a heating device, such as a microwave oven, to allow chilled food, e.g., such as sandwiches, to be heated to a desirable temperature before consumption.
Typically, the dispensable items are maintained within a chamber that is thermally insulated from the exterior of the vending machine. A cooling system withdraws heat from the chamber. The cooling system can include an evaporator, a compressor, a condenser, and a metering (flow constricting) device.
When the cooling system is on, coolant liquid, e.g., Freon, enters the evaporator. The evaporator is thermally coupled to the refrigerated chamber. The coolant liquid is generally colder than the chamber so that the coolant removes heat from the chamber. The liquid evaporates as it absorbs the heat.
The evaporated coolant is pumped out of the evaporator through a suction line by a compressor. The compressor increases the pressure of the coolant, raising its temperature in the process. The pressurized coolant is then directed to a condenser via a discharge line.
The condenser couples the coolant to a chilled environment. This causes the coolant to give up heat and condense into a liquid. The liquid flows through a liquid line, including the flow meter (which is basically a flow restriction) back to the evaporator to begin another cooling cycle.
The evaporator removes heat from the nearby chamber air. To ensure that the cool air reaches the dispensable items and to ensure a uniform temperature within the chamber, the chamber air is circulated. Generally, one or more fans are operated within the chamber interior to effect this circulation.
One or more thermo-sensors monitor the temperature inside the chamber. Typically, there is a desired temperature range for the vended items, for example, 0xc2x0-2xc2x0 C. (xcx9c32xc2x0-36xc2x0 F.) for sodas. When the chamber temperature reaches the higher threshold, the compressor is activated and the cooling process begins. When the chamber temperature falls to the lower threshold, the compressor is turned off, and cooling effectively halts. Another cooling cycle can begin when the temperature reaches the upper threshold due to inevitable heat transfer through the chamber wall.
Refrigerated vending machines consume considerable electric power. Typically, most of the power consumed by a refrigerated vending machine is consumed by the cooling system, and especially by the compressor, even though it is not operated continuously. However, the fans, the dispensing mechanism, the money handling mechanisms, panel lights, sensors, and control electronics all consume power. For reasons of energy conservation and cost, it is desirable to be able to reduce the energy consumed by a refrigerated vending machine without adversely affecting its service (to patrons) and its economic (to the vending machine owner) aspects.
The most straightforward approach to saving energy is to disconnect AC power. For example, a vending machine could be turned off during non-business hours, e.g., from 10 pm to 6 am. To avoid the inconvenience of manual activation and inactivation, an external timer can be used to control AC power to the vending machine. However, whether power to the vending machine is switched by a human operator or a timer, potential patrons are denied dispensable items during off hours.
Parent patent application Ser. No. 09/182,586 discloses an external power control system for a vending machine that includes an occupancy sensor. This can be used to ensure a vending machine is on whenever people are in its vicinity. An ambient thermo-sensor can also be included to determine a reactivation time to prevent the dispensable items from become unacceptably warm.
Using even an effective external device is not ideal. From a manufacturing viewpoint, there is duplication of components. For example, the external power controller must have its own housing, its own power supply, and own control electronics. Also, the vending machine operator must manage two devices instead of one. From a power-conservation standpoint, power is less likely to be saved if it requires a separate device to be purchased, installed, and set up. Accordingly, refrigerated vending machines with built-in power-conservation features are desired.
On approach allows a vending machine to be programmed to allow different target cooling set points at different times. in this case, for example, a vending machine can be programmed to have a higher set point during periods of expected inactivity (e.g., non-business hours). Raising the set point can have a significant impact on power consumption since power is consumed roughly in proportion to the differential between the ambient temperature and the desired chamber temperature. When the set point is higher, the compressor duty cycle is reduced, thus reducing overall power consumption.
This varying set-point approach is attractive in that the vending machine is always on and ready to do business. The dispensable items are warmer than ideal, but only by an amount determined by variations in the set point. However, there is generally not much latitude for raising set points.
The set points used in normal operation are typically chosen carefully to achieve optimal cooling of dispensable items without wasting power. Power savings beyond those achieved during normal operation typically exact a penalty, e.g., possibly compromising the freshness or taste of the dispensable items. What is needed is a system that provides for power conservation without adverse affects on the dispensable items.
The present invention provides for normal and power-conservation modes of operation. During normal operation, the average chamber temperature is maintained within an optimal range, and the spatial variance of the temperature is kept relatively small. During power-conservation mode, the average chamber temperature is allowed to rise above the optimal range, and the temperature variance is allowed to increase. Due to the increase in temperature variance, the minimum temperature rises, if at all, more slowly than the average temperature. A patron""s expectation for a chilled item can be met by dispensing items stored in a relatively cool zone of the chamber even when the average chamber temperature is above the optimal range.
In effect, power is conserved by reducing the volume of the chamber maintained at the desired temperature. This allows at least some dispensable items to remain within a desired temperature range even while the average temperature in the enclosing chamber exceeds the desired temperature. In general, temperature variance can be increased simply by turning off forced circulation, e.g., turning off fans. The items that most require maintenance of the desired temperature, either to preserve freshness or for optimal taste, are preferably located in a xe2x80x9ccool zonexe2x80x9d instead of a xe2x80x9cwarm zonexe2x80x9d.
In normal-operation mode, forced circulation of air or other heat transfer medium promotes a relatively uniform (low-variance) temperature distribution throughout the refrigerated chamber. Of course, it is not necessary that circulation be forced all the time during normal operation, but it should be forced most of the time during normal operation even when the cooling system is off (i.e., the cooling system is not expending energy to remove heat from the chamber). In power-conservation mode, forced-air circulation is avoided most of, if not all, the time the cooling system is off. However, forced-air circulation can be used while the cooling system is on to transfer heat from the chamber interior to the cooling system for removal from the chamber. While forced-air circulation is off, the chamber air stratifies to define the warm and the cool zones.
In one realization of the invention, items are arranged so that cooler items will be dispensed before warmer items. For example, a soda vending machine can arrange soda cans in stacks, and dispense from the bottom of the stacks. In this case, the stack bottoms can be in the cool zone, while the stack tops can be in the warm zone. Thus, a patron requesting a soda after an extended period of power-conservation mode operation receives a soda that is cooler than the average soda at the time of the request.
The invention provides for combining this preferential cooling approach with activity detection. Activity can be detected when money is inserted into the vending machine or, more predictively, using an occupancy sensor. In either case, the detected activity can trigger a transition from power-conservation mode to normal mode. A complementary lack of activity determination can reinstate the power-conservation mode. The algorithm for switching modes can also include absolute-time, e.g., time-of-year, determinations.
In the soda example, the cans to be dispensed next are kept the coolest. There are alternative criteria for determining which items to keep coolest. For example, items most requiring cold to maintain freshness, e.g., tuna sandwiches, can be stored at the bottom of the refrigerated chamber. Items that can remain fresh and tasty at higher temperatures, e.g., potato chips, are stored in a higher region of the chamber. In this case, the vending machine can employ horizontal rather than vertical dispensing.
A test relating to the invention yielded the surprising result that, after a two-hour interval in power-savings mode, soda cans at the bottom of respective stacks were colder than they were at the beginning of the interval. This test demonstrates the viability of the inventive approach in practice.
As long as normal mode is resumed with the advent of activity, considerable power can be saved without any penalty in practice. Serendipitously, the invention provides for further savings: since circulation fans are off in power conservation mode, they do not consume power, so overall power consumption is reduced. Moreover, since the fans are off, they do not dissipate heat into the refrigerated chamber; thus they do not aggravate the average temperature rise during power conservation mode. These and other features and advantages of the invention are apparent from the description below with reference to the following drawings.